Arsenal suffered a second heavy defeat in the space of a week as Brighton took advantage of defensive mistakes to dent the Gunners' hopes of a second-place finish.
Brighton had lost all 13 of their previous Women's Super League games against Arsenal but a Jelena Cankovic double, sandwiched by goals from Fran Kirby and Kiko Seike, secured a well-deserved victory.
Kirby gave Brighton a 16th minute lead with a stunning curled effort from the edge of the box, though the way Beth Mead surrendered possession before Leah Williamson hesitated in closing down Cankovic typified Arsenal's shaky start.
That said, Alessia Russo went close to providing the perfect response as her close-range header cannoned back off the post just a minute later.
Brighton goalkeeper Baggaley - a late addition to the line up in place of Melina Loeck - became very busy all of a sudden, denying both Frida Maanum and Kim Little from close range in quick succession.
The 28-year-old produced a masterful stop when Foord met Caldentey's cross from six yards out, but couldn't prevent the ball falling back to Foord to slam home.
Arsenal continued to push as Mariona and Maanum both tested Baggaley from outside the area, but it was the hosts that went into the break in control.
A Seagulls corner was headed out to the edge of the box, where Cankovic sent a fizzing first-time volley past a helpless Zinsberger.
Arsenal started the second half in the same wobbly way in which they began the first - Nikita Parris reached a long ball before Zinsberger but could only poke it wide.
If that was a warning not to overcomplicate things, it was one Renee Slegers' side didn't heed.
Zinsberger's attempted ball out to the wing under pressure was easily intercepted and played to an unmarked Cankovic. Not a single defender was in touching distance of the Serbian midfielder as she lobbed the ball over Zinsberger and into the unguarded goal.
Arsenal's defending got even worse 90 seconds later - Katie McCabe dropped deep when her defensive colleagues pushed high, allowing Brighton striker Seike to race through on goal and finish expertly past Zinsberger.
Caldentey pulled a goal back with a curled effort in injury time, before Jenna Nighswonger hit the crossbar from distance, but it wasn't enough.
A second successive defeat leaves Arsenal just a point ahead of third-placed Manchester United going into the final day of the season, while Brighton look set to achieve a club-best fifth place finish.
